Makefile object lists and object locations

Question

I have my object files compiled into a specific location using these variables and targets:

OBJDIR=./obj

objdir:
    $(MKDIR) $(OBJDIR)

%.o: %.cpp objdir
    $(CXX) $(CXXFLAGS) -c $< -o $(OBJDIR)/$@

Now my problem is, when it comes to linking the executable, I want to use variables to hold the lists of object files, such as:

FOOOBJECTS=foo.o foo1.o foo2.o
BAROBJECTS=bar.o bar1.o

mycrappyprogram: main.o $(FOOBOJECTS) $(BARBOJECTS)
    $(CXX) $(FOOBJECTS) $(BAROBJECTS) -o $(BINDIR)/mycrappyprogram

Of course I can't do this because all the objects are in ./obj/ so the recipe can't find them.

How can I define a list of object files once, and have them be qualified when used in the recipe?

Answer 1

1) Make can manipulate strings:

FOOOBJECTS=foo.o foo1.o foo2.o
BAROBJECTS=bar.o bar1.o

OBJECTS = $(addprefix $(OBJDIR)/, $(FOOOBJECTS) $(BAROBJECTS))

2) Automatic variables are your friends (and I presume you want your executable to incorporate main.o, and not just the foo and bar objects):

mycrappyprogram: main.o $(OBJECTS)
    $(CXX) $^ -o $(BINDIR)/$@

3) A (non-PHONY) rule should build the very thing it says it will build, or you'll get into trouble:

$(BINDIR)/mycrappyprogram: main.o $(OBJECTS)
    $(CXX) $^ -o $@

$(OBJDIR)/%.o: %.cpp objdir
    $(CXX) $(CXXFLAGS) -c $< -o $@